1. Field of the Invention
The invention relates to a method for folding sheet-shaped elements in a folding station of a folding machine, in which the folding station has at least one folding unit and the sheet elements are supplied to the folding station in a transport direction with their leading edge in front and with an overlap. The invention also relates to a folding machine for folding sheet-shaped elements of paper, paperboard and the like, in particular for implementing the method according to the invention, having at least one first and one second folding station, each having driven folding rolls, a transport device disposed between the first and second folding stations, a drive and a common control unit connected to the drives.
2. Description of the Related Art
Firstly, pocket folding machines are known from the prior art. The structure of a pocket folding machine having a large number of pocket folding units is disclosed in German Published, Non-Prosecuted Patent Application DE 10 2004 041 471 A1. A respective pocket folding unit thereof includes a folding pocket and three folding rolls, which are disposed in two pairs of folding rolls. Furthermore, blade folding machines are known. German Published, Non-Prosecuted Patent Application DE 29 40 360 A1 discloses a single-blade folding unit for folding printed and pre-folded sheets. In combined folding machines, pocket folding units and blade folding units are combined. In that case, parallel folds are folded in pocket folding units in a first folding station, and cross folds are folded in blade folding units in a following folding station. German Published, Non-Prosecuted Patent Application DE 10 2006 055 301 A1 shows combined folding machines having a plurality of pocket folding units and blade folding units disposed downstream.
In order to increase the output of folding machines, which means their productivity, the speed of passage of the sheets through the folding machine is normally increased. However, as a result of the increase in the speed, a respective folded sheet experiences deformation and damage, which leads to considerable costs in terms of quality.
German Published, Non-Prosecuted Patent Application DE 103 36 757 A1 reveals methods for folding sheets supplied overlapping in the form of an imbricated stream. As a result of the application of the method, the productivity of the folding machines is intended to be increased without increasing the speed of passage of the sheets through the machine. To that end, folding gap widths of infeed folding rolls are enlarged or reduced as a function of a folding cycle in partial phases of a continuous folding operation. Such a procedure is disadvantageous since, in order to adapt the folding gap width, firstly a complicated mechanical mounting of the folding rolls and also complicated activation of the drives for adapting the folding gap width are necessary. It is further disadvantageous that sheets following one another meet in the folding units and are moved at a different speed relative to one another. In the process, the sheets can be damaged and it is possible for so-called markings to occur. As a result of the relative movement of the two sheets, increased folding tolerances, electrostatic charging and disruption in the area of the pocket infeed can be caused.